Shaping method for producing shaped bodies with at least one surface that has self-cleaning properties, and shaped bodies produced according to this method

ABSTRACT

The invention relates to shaping processes for producing moldings with at least one surface which has self-cleaning properties and has elevations formed by microparticles, by thermal shaping of materials comprising organic compounds by means of a mold, and also to the resultant moldings. The process of the invention generates surfaces with self-cleaning properties by, prior to the thermal shaping, applying microparticles to the inner surfaces of the mold and then carrying out the molding process, in which the microparticles are pressed into and anchored into the surface of the molding, where this surface has not yet solidified. The process of the invention may be used in thermal shaping processes selected from blow molding, extrusion blow molding, extrusion stretch blow molding, injection blow molding, injection stretch blow molding, thermoforming, vacuum stretch forming, pressure stretch forming, and rotary thermoforming. The process is suitable for producing three-dimensional articles, such as bottles, housing parts, drums, and many other items. The process of the invention is very simple, since it makes use of existing equipment. The process of the invention gives access to self-cleaning surfaces which have particles with a fissured structure, without any need to apply an additional emboss layer or foreign-material carrier layer to the moldings.

The present invention relates to molding processes for producingmoldings with at least one surface which has self-cleaning propertiesand has elevations formed by microparticles, by thermal shaping ofmaterials comprising organic compounds by means of a mold and also tomoldings thus produced.

Various processes for treating surfaces making the surfaces dirt- andwater-repellent have been disclosed in surface technology. For example,it is known that if a surface is to be given good self-cleaningproperties it has not only to be hydrophobic but to have a certainroughness. A suitable combination of structure and hydrophobicproperties makes it possible for even small amounts of water set inmotion on the surface to entrain adherent dirt particles and clean thesurface (WO 96/04123; U.S. Pat. No. 3,354,022, C. Neinhuis, W.Barthlott, Annals of Botany 79. (1997), 667).

As early as 1982, A. A. Abramson described, in Chimia i Shisn russ. 11,38, the roll-off of water droplets from hydrophobic surfaces, especiallyif they have structuring, even at extremely low inclinations, but therewas no recognition there of self-cleaning properties.

The prior art of EP 0 933 388 requires an aspect ratio greater than 1and surface energy of less than 20 mN/m for self-cleaning surfaces, theaspect ratio being defined as the quotient calculated by dividing theaverage height of the structure by its average width. The abovementionedcriteria are to be found in the natural world, for example in the lotusleaf. The 30′ surface of the plant, formed from a hydrophobic waxymaterial, has elevations, the distance between which is a few μm. Waterdroplets essentially contact only the peaks of the elevations. There aremany descriptions in the literature of water-repellent surfaces of thistype. An example here is an article in Langmuir 2000, 16, 5754, byMasashi Miwa et al., stating that contact angle and roll-off angleincrease with increased structuring of artificial surfaces formed fromBoehmite, applied to a spin-coated layer and then calcined.

Swiss Patent 268258 describes a process in which structured surfaces aregenerated by applying powders, such as kaolin, talc, clay, or silicagel. The powders are secured to the surface by way of oils and resinsbased on organosilicon compounds.

It is known that hydrophobic materials, such as perfluorinated polymers,can be used to produce hydrophobic surfaces. DE 197 15 906 A1 describesthe use of perfluorinated polymers, such as polytetrafluoroethylene, orcopolymers made from polytetrafluoroethylene with perfluorinated alkylvinyl ethers, to generate hydrophobic surfaces which have structuringand have low adhesion to snow and ice. JP 11171592 describes awater-repellent product and its production, the dirt-repellent surfacebeing produced by applying, to the surface to be treated, a film whichcomprises fine particles made from metal oxide and comprises thehydrolyzate of a metal alkoxide and, respectively, of a metal chelate.To secure the film, the substrate to which the film has been applied hasto be sintered at temperatures above 400° C. This process is thereforeuseful only for substrates which can be heated to temperatures above400° C.

The processes conventionally used hitherto for producing self-cleaningsurfaces are complicated and in many cases have only limited usefulness.For example, embossing techniques are an inflexible method of applyingstructures to three-dimensional bodies of varying shapes. There is stillcurrently no suitable technology for generating flat coating films oflarge surface area. A disadvantage of processes in whichstructure-forming particles are applied to surfaces by means of acarrier—e.g. an adhesive—is that the resultant surfaces are composed ofa great variety of combinations of materials which, for example, havedifferent coefficients of thermal expansion, the possible result beingdamage to the surface.

It was therefore an object of the present invention to provide a processfor producing self-cleaning surfaces on three-dimensional moldings. Themaximum simplicity of technology should be used here, and theself-cleaning surfaces should be durable.

Surprisingly, it has been found that when hydrophobic, nanostructuredparticles are applied to the inner mold surfaces of molds for thermalshaping, and then molding a molding by using this mold, the particlescan be firmly anchored to the surface of the molding.

The present invention therefore provides a shaping process for producingmoldings with at least one surface which has self-cleaning propertiesand has elevations formed by microparticles, by thermal shaping ofmaterials comprising organic compounds by means of a mold, characterizedin that, prior to the thermal shaping process, microparticles areapplied to the inner surfaces of the mold, and the shaping process isthen carried out, in which the microparticles are pressed into andanchored into the surface, which has not yet solidified, of the molding.

The present invention also provides moldings with at least one surfacewhich has self-cleaning properties and has surface structures withelevations, produced by the process of the invention.

An advantage of the process of the invention is that it can utilizeexisting equipment for producing moldings by thermal shaping. The usualmethod of producing moldings of this type is that the material to beprocessed is softened or melted and a mold is used to mold thismaterial. The process of the invention utilizes this process insofar as,prior to the actual shaping process, microparticles are applied to themold, and are transferred to the molding during the shaping process, bypressing the particles into the softened or molten surface of themolding. This simple: method gives access to moldings with self-cleaningsurfaces which have particles with a fissured structure, without anyneed to apply an additional emboss layer or foreign-material carrierlayer to the moldings.

An advantage of the moldings of the invention is that structure-formingparticles are not secured by a carrier material, thus avoiding anunreasonably high number of combinations of materials and the adverseproperties associated therewith.

The process of the invention gives access to self-cleaning moldings inwhich the self-cleaning properties are not achieved by virtue of anyadditional application of material for securing the particles, or byvirtue of any additional chemical process.

Another advantage of the process of the invention is that surfacessusceptible to scratching are not damaged by subsequent mechanicalapplication of a carrier layer and/or of particles.

A circumstance which proves to be very particularly advantageous is thatany desired surfaces which can be produced by thermal shaping processescan be rendered self-cleaning. Another advantage is the demoldability offine-structured moldings. This cannot always be reliably provided bystructured molds.

The invention is described below by way of example, but is not limitedto these embodiments.

A feature of the shaping process of the invention for producing moldingswith at least one surface which has self-cleaning properties and haselevations formed by microparticles, by thermal shaping of materialscomprising organic-compounds, by means of a mold, is that, prior to thethermal shaping, microparticles are applied to the inner surfaces of themold, and then the shaping process is carried out, in which themicroparticles are at least to some extent pressed into and anchoredinto the surface, which has not yet solidified, of the molding. The moldis preferably a mold which is usually used for producing conventionalmoldings. These conventional molds may, for example, be composed of twoparts, the cavity and the core. In the process of the invention, themicroparticles may be applied to the cavity (female mold) and/or to thecore (male mold). During the shaping process, the microparticles are atleast to some extent pressed into the molding composition, and arefirmly held by the molding composition when it solidifies, and are thusanchored, giving particularly stable anchoring if the microparticlesused have a fine structure on the surface, since, the fine structure isto some extent filled by the molding composition and many anchoringpoints are present once the composition has solidified. The surfaceproduced by the process of the invention with self-cleaning propertiesand microparticles on the surface which form elevations may have beendesigned so that the surface exclusively has microparticles, or almostexclusively has microparticles, or else has microparticles whoseseparation from one another is from 0 to 10 particle diameters, inparticular from 0 to 3 particle diameters.

The process of the invention can use a very wide variety of knownthermal shaping processes in which the molding composition is softenedor melted by introducing thermal energy and then a mold is used to moldthis composition. The thermal shaping process is preferably one selectedfrom blow molding, extrusion blow molding, extrusion stretch blowmolding, injection blow molding, injection stretch blow molding,thermoforming, vacuum stretch forming, pressure stretch forming, androtary thermoforming. The nature of the actual conduct of theseprocesses is known per se. Examples of descriptions of these thermalshaping processes may be found in: Kunststoff Handbuch 1, DieKunststoffe; Chemie, Physik, Technologie [Plastics Handbook 1, ThePlastics; Chemistry, Physics, Technology], Bodo Carlowitz (Editor),Hanser Verlag Munich 1990, or in Hans Batzer, Polymere Werekstoffe[Polymeric materials], Georg Thieme Verlag Stuttgart—New York, 1984, andalso in the references cited within these references. They also givedescriptions of equipment, starting materials, and process parametersfor the conduct of the thermal shaping processes, and these need nottherefore be described here in any further detail.

The material comprising organic compounds and used as moldingcomposition may comprise any of the materials which comprise polymerblends or polymers suitable for thermal shaping. The material comprisingorganic compounds and used in the process of the invention is preferablya material comprising a natural rubber or a synthetic rubber, or avulcanized rubber, or, as a mixture or individually, and as homopolymeror copolymer, polynorbornene, or acrylonitrile-butadiene-styreneterpolymers (ABS), or poly(4-methyl-11-pentene), or polyisobutene, orpoly(vinylidene fluoride), or polyalkylene terephthalates, in particularpolyethylene terephthalate or polybutylene terephthalate (PET or PBT),or polyacrylonitrile, or polyether sulfones, or polyesters, orpolystyrenes, or cyclic polyalkenes, or aliphatic linear or branchedpolyalkenes, or polypropylenes, or polyethylenes, or polyvinyl chloride,or polyamides, or poly(meth)acrylates, or polycarbonates, in a polymer.In this context, the skilled worker is aware that certain of theabovementioned materials can be used only for certain shaping processes.From the thermoplastic polymers group, those particularly suitable forblow molding are PVC and polypropylene, and those particularly suitablefor extrusion blow molding, extrusion stretch blow molding, injectionblow molding, and injection stretch blow molding are PET,polycarbonates, e.g. Makrolone® grades, and polypropylenes, and thoseparticularly suitable for thermoforming, vacuum stretch forming,pressure stretch forming, and rotary thermoforming are polypropyleneABS, and PVC.

The impression process involved in the process of the invention ispreferably conducted so that at least some of the particles, preferablyat least 50% of the particles, are pressed into the softened or moltensurface of the molding to the extent of not more than 90% of theirdiameter, preferably using from 10 to 70%, with preference using from 20to 50%, and very particularly preferably using from 30 to 40%, of theiraverage particle diameter. The surface of the molding into which themicroparticles are pressed and anchored, where this surface has not yetsolidified, may be the surface of a melt of a material to be molded, orthe softened surface of a material to be molded.

The microparticles which are pressed into the surface of the molding inthe process of the invention are applied, prior to the process ofimpression via shaping, to the surface of the mold, or to at least oneportion of a mold. Depending on the thermal shaping process used, and onthe mold used, it can be advantageous for microparticles to be appliedonly to those surfaces of the mold which, during shaping of thesubsequent molding, e.g. a vessel or a bottle, come into contact with anexternal and/or an internal surface of the molding. This permits theproduction of articles which have surfaces with self-cleaning propertieseither on their inner sides or on their outer sides, or on the inner andouter sides. In particular during injection stretch blow molding, whichis used for example to produce moldings with rotational symmetry (hollowarticles), e.g. to produce bottles, it can be advantageous to applymicroparticles to the mold core used to produce the inside of a parison.Despite subsequent blowing of the parison, the final product has innersurfaces with elevations, and these have self-cleaning properties.

The preferred method of application is spraying. Application of themicroparticles to the mold is advantageous particularly because themicropowder inhibits adhesion of the material of the molding to the moldonce the molding procedure has ended, since there is little, or no,contact of the material itself with the mold, because the microparticlesare applied very densely to the mold to achieve the preferredseparations of the elevations.

Examples of methods of spray-application of the microparticles to themold are spray-application of microparticle-powder-containing aerosolsor dispersions which, besides the microparticles, comprise a propellantor a preferably highly volatile solvent, preference being given tospray-application from suspensions. The solvent preferably present inthe suspensions used is an alcohol, in particular ethanol orisopropanol, ketones, e.g. acetone or methyl ethyl ketone, ethers, e.g.diisopropyl ether, or else hydrocarbons, such as cyclohexane. Thesuspensions particularly preferably comprise alcohols. It can beadvantageous for the suspension to comprise from 0.1 to 10% by weight,preferably from 0.25 to 7.5% by weight, and very particularly preferablyfrom 0.5 to 5% by weight, of microparticles, based on the total weightof the suspension. In particular in the case of spray-application of adispersion, it can be advantageous for the mold to have a mold surfacetemperature of from 30 to 150° C. Depending on the molding to beproduced or on the material used therefor, however, the temperature ofthe mold may also be any temperature in the range mentioned,irrespective of the microparticle powder or the application of themicroparticle powder.

The microparticles used in the process of the invention are preferablythose which comprise at least one material selected from silicates,minerals, metal oxides, metal powders, silicas, pigments, and polymers.It is preferable to use microparticles whose diameter is from 0.02 to100 μm, particularly preferably from 0.1 to 50. μm, and veryparticularly preferably from 0.1 to 30 μm. It is also possible to usemicroparticles with diameters below 500 nm. However, other suitablemicroparticles are those accreted from primary particles to giveagglomerates or aggregates whose size is from 0.2 to 100 μm.

The microparticles used, in particular the particles whose surface hasan irregular fine structure in the nanometer range, are particles whichcomprise at least one compound selected from fumed silica, precipitatedsilicas, aluminum oxide, mixed oxides, doped silicates, titaniumdioxides, and pulverulent polymers. Preferred particles whose surfacehas an irregular fine structure in the nanometer range have, within thisfine structure, elevations whose aspect ratio is greater than 1,particularly preferably greater than 1.5, and very particularlypreferably greater than 2.5. The aspect ratio is in turn defined as thequotient calculated by dividing the maximum height of the elevation byits maximum width.

The microparticles preferably have hydrophobic properties, which may beattributable to the properties of the materials present on the surfacesof the particles, or else be obtained by treating the particles with asuitable compound. The particles may be provided with hydrophobicproperties prior to or after the process of pressing into the surface.

For the hydrophobicization of the microparticles prior to or after theprocess of pressing (anchoring) into the surface of the molding, thesemay be treated with a compound suitable for hydrophobicization, e.g. oneselected from the alkylsilanes, the fluoroalkylsilanes, and thedisilazanes, for example those supplied as Dynasylan by Degussa AG.

The microparticles whose use is preferred are described in more detailbelow. The particles used may come from a variety of sectors. Forexample, they may be titanium dioxides, doped silicates, minerals, metaloxides, aluminum oxide, silicas, fumed silicates, Aerosils® orpulverulent polymers, e.g. spray-dried and agglomerated emulsions, orcryogenically milled PTFE. Particularly suitable particle systems arehydrophobicized fumed silicas, known as Aerosils. To generate theself-cleaning surfaces, hydrophobic properties are needed alongside thestructure. The particles used may themselves be hydrophobic, for examplePTFE. The particles may have been provided with hydrophobic properties,for example Aerosil VPR 411®, or Aerosil R. 8200®. However, they mayalso be hydrophobicized subsequently. It is unimportant here whether theparticles are hydrophobicized prior to application or after application.Examples of these particles which have to be hydrophobicized areAeroperl P 90/30®, Sipernat silica 350, Aluminum oxide C®, Zirconiumsilicate, vanadium-doped or. VP Aeroperl P 25/20®. In the case of thelatter, it is advantageous for the hydrophobicization to take place bytreatment with perfluoroalkylsilane compounds followed byheat-conditioning.

The process of the invention can produce moldings with at least onesurface which has self-cleaning properties and has surface structureswith elevations. A feature of these moldings with at least one surfacewhich has self-cleaning properties is that the surface has at least onefirmly anchored layer of microparticles which form elevations. Thepresence of elevations on at least portions of the surface of themoldings, in combination with hydrophobic properties, ensures that theseregions of the surface are difficult to wet and therefore haveself-cleaning properties. The securely anchored layer of microparticlesis obtained by applying microparticles in the form of a layer to themold prior to the shaping process, and then using this mold for molding.During the shaping process, the microparticles are pressed at least tosome extent into the molding composition, and are securely held andtherefore anchored by the molding composition when it solidifies, givingparticularly stable anchoring if the microparticles used have a finestructure in the surface, since the fine structure is to some extentfilled by the molding composition, and many anchoring points are presentonce the molding composition has solidified. For the purposes of thepresent invention, a layer of microparticles is a collection ofmicroparticles forming elevations on the surface. The design of thelayer may be such that the surface exclusively has microparticles, oralmost exclusively has microparticles, or has microparticles whoseseparation from one another is from 0 to 10 particle diameters, inparticulars from 0 to 3 particle diameters.

The surfaces of the moldings with self-cleaning properties preferablyhave at least one layer with elevations with an average height of from20 nm to 25 μm and with an average separation of from 20 nm to 25 μm,preferably with an average height of from 50 nm to 10 μm and/or with anaverage separation of from 50 nm to 10 μm, and very particularlypreferably with an average height of from 50 mm to 4 μm and/or with anaverage separation of from 50 nm to 4 μm. The moldings of the inventionvery particularly preferably have surfaces with elevations with anaverage height of from 0.25 to 1 μm and with an average separation offrom 0.25 to 1 μm. For the purposes of the present invention, theaverage separation of the elevations is the separation between thehighest elevation of one elevation and the nearest highest elevation. Ifthe elevation is a cone, the peak of the cone is the highest elevationof the elevation. If the elevation is a rectangular parallelepiped, theuppermost surface of the parallelepiped is the highest elevation of theelevation.

The wetting of bodies, and therefore the self-cleaning property, can bedescribed via the angle of contact made by a water droplet with thesurface. An angle of contact of 0 degree here means complete wetting ofthe surface. The static angle of contact is generally measured usingequipment in which the angle of contact is determined optically. Staticcontact angles below 125° C. are usually measured on smooth hydrophobicsurfaces. The present moldings with self-cleaning surfaces have staticcontact angles which are preferably above 130°, with preference above140°, and very particularly preferably above 145°. In addition, it hasbeen found that a surface has good self-cleaning properties only when itexhibits a difference of not more than 10° between advancing andreceding angle, and for this reason surfaces of the invention preferablyhave a difference of less than 10°, preferably less than 5°, and veryparticularly preferably less than 4°, between advancing and recedingangle. To determine the advancing angle, a water droplet is placed onthe surface by means of a cannula, and the droplet is enlarged on thesurface by adding water through the cannula. During enlargement, themargin of the droplet glides over the surface, and the contact angledetermined is the advancing angle. The receding angle is measured on thesame droplet, but water is removed from the droplet through the cannula,and the contact angle is measured during reduction of the size of thedroplet. The difference between the two angles is termed hysteresis. Thesmaller the difference, the smaller the interaction of the water dropletwith the surface of the substrate, and therefore the better the lotuseffect.

The aspect ratio for the elevations of the surfaces of the inventionwith self-cleaning properties is preferably greater than 0.15. Theelevations formed by the particles themselves preferably have an aspectratio of from 0.3 to 0.9, particularly preferably from 0.5 to 0:8. Theaspect ratio is defined here as the quotient calculated by dividing themaximum height of the structure of the elevations by its maximum width.

In the moldings of the invention with surfaces which have self-cleaningproperties and have surface structures with elevations, the surfaces arepreferably synthetic polymer surfaces into which particles have beendirectly incorporated or directly anchored, and have not been bonded viacarrier systems or the like.

The particles are bonded or anchored to the surface in that theparticles are pressed into the molten or softened material of themolding or of the molding composition during process. An advantageousmethod of achieving the aspect ratios mentioned is that at least some ofthe particles, preferably more than 50%, more preferably more than 75%of the particles, are preferably pressed into the surface of the moldingonly to the extent of 90% of their diameter. The surface thereforepreferably has particles which have been anchored in the surface usingfrom 10 to 90%, preferably from 20 to 50%, and very particularlypreferably from 30 to 40%, of their average particle diameter, and partsof whose inherently fissured surface therefore still protrude from themoldings. This method ensures that the elevations formed by theparticles themselves have a sufficiently large aspect ratio, preferablyat least 0.15. This method also ensures a very lasting bond, between thesecurely bonded particles and the surface of the molding. The aspectratio here is defined as the ratio of maximum height of the elevationsto their maximum width. According to this definition, the aspect ratiofor a particle assumed to be ideally spherical and projecting to anextent of 70% from the surface of the molding is 0.7. It should beexpressly pointed out that the particles of the invention do not have tobe of spherical shape.

The microparticles securely bonded to the surface and forming theelevations on the surface of the moldings have preferably been selectedfrom silicates, minerals, metal oxides, metal powders, silicas,pigments, and polymers, very particularly preferably from fumed silicas,precipitated silicas, aluminum oxide, mixed oxides, doped silicates,titanium dioxides, and pulverulent polymers.

Preferred microparticles have a diameter of from 0.02 to 100 μm,particularly preferably from 0.1 to 50 μm, and very particularlypreferably from 0.1 to 30 μm. However, suitable microparticles may alsohave a diameter below 500 nm, or be formed by accretion of primaryparticles to give agglomerates or aggregates with a size of from 0.2 to100 μm.

Particularly preferred microparticles which form the elevations of thestructured surface of the inventive molding are those whose surface hasan irregular, slightly fissured fine structure in the nanometer range.These microparticles with the irregular, slightly fissured finestructure preferably have elevations with an aspect ratio greater than 1in the fine structures, particularly preferably greater than 1.5. Theaspect ratio is in turn defined as the quotient calculated by dividingthe maximum height of the elevation by its maximum width. FIG. 1 givesan illustrative diagram of the difference between the elevations formedby the particles and the elevations formed by the fine structure. Thefigure shows the surface of a thermoformed molding X, which hasparticles P (only one particle being depicted in order to simplify thepresentation). The elevation formed by the particle itself has an aspectratio of about 0.71, this being the quotient calculated by dividing themaximum height mH of the particle, which is 5, since only that portionof the particle which protrudes from the surface of the molding Xcontributes to the elevation, by its maximum width mB, which in turn is7. A selected elevation of the elevations E present on the particles byvirtue of their fine structure has an aspect ratio of 2.5, this beingthe quotient calculated by dividing the maximum height mH of theelevation, which is 2.5, by its maximum width mB, which in turn is 1.

Preferred microparticles whose surface has an irregular fine structurein the nanometer range are those particles which comprise at least onecompound selected from fumed silica, precipitated silicas, aluminumoxide, mixed oxides, doped silicates, titanium dioxides, and pulverulentpolymers.

It can be advantageous for the microparticles to have hydrophobicproperties, which may be attributable to the properties of the materialpresent on the surfaces of the particles, or else may be obtained bytreating the particles with a suitable compound. The microparticles maybe provided with hydrophobic properties prior to or after application orbonding to the surface of the molding. To hydrophobicize the particlesprior to or after application to the surface, they may be treated with acompound suitable for hydrophobicization, e.g. selected from the groupof the alkylsilanes, the fluoroalkylsilanes, and the disilazanes.

Particularly preferred microparticles are described in more detailbelow. The particles may be derived from various fields. For example,they may be silicates doped silicates, minerals, metal oxides, aluminumoxide, silicas, or titanium dioxides, Aerosils®, or pulverulentpolymers, e.g. spray-dried and agglomerated emulsions, or cryogenicallymilled PTFE. Particularly suitable particle systems are hydrophobicizedfumed silicas, known as Aerosil® grades. To generate the self-cleaningsurfaces, hydrophobic properties are needed along side the structure.The particles used may themselves be hydrophobic, for examplepulverulent polytetrafluoroethylene(PTFE). The particles may have beengiven hydrophobic properties, for example Aerosil VPR 411® or Aerosil R8200®. However, they may also be hydrophobicized subsequently. It isunimportant here whether the particles are hydrophobicized prior toapplication or after application. Examples of these particles which haveto be hydrophobicized are Aeroperl 90/30®, Sipernat silica 350®,Aluminum oxide C®, Zirconium silicate, vanadium-doped or VP Aeroperl25/20®. In the case of the latter, it is advantageous for thehydrophobicization to take place by treatment with perfluoroalkylsilanecompounds followed by heat-conditioning.

The moldings may have the elevations on all surfaces or only on certainsurfaces, or on subregions of these. The moldings of the inventionpreferably have the elevations on all surfaces or on all inner and/orouter surfaces.

The material of the moldings may preferably comprise polymers or polymerblends based on polycarbonates, on polyoxymethylenes, onpoly(meth)acrylates, on polyamides, on polyvinyl chloride (PVC), onpolyethylenes, on polypropylenes, on polystyrenes, on polyesters, onpolyether sulfones, on aliphatic linear or branched polyalkenes, oncyclic polyalkenes, on polacrylonitrile, or on polyalkyleneterephthalates, or else a mixture of these, or copolymers. The materialof the moldings is particularly preferably a material selected frompoly(vinylidene fluoride), or is another polymer selected frompolyethylene, polypropylene, polyisobutene, poly(4-methyl-1-pentene),and polynorbornene, in the form of homo- or copolymer. The material forthe surface of the molding is very particularly preferably a materialcomprising a natural rubber, or a synthetic rubber, or a vulcanizedrubber, or poly(vinylidene fluoride), or polybutylene terephthalate, orpolyethylene terephthalate, or acrylonitrile-butadiene-styreneterpolymers (ABS), polyesters, polystyrenes, polymethyl methacrylates,polypropylene, or polyethylene.

The process of the invention gives access to three-dimensional moldingswith a surface which at least in part has self-cleaning properties andhas surface structures with elevations. The moldings may have anydesired shape which can be produced by the known processes of thermalshaping. These moldings may in particular be vessels for receivingliquids or pastes. These moldings may in particular be those selectedfrom vessels, lampshades, bottles, automotive tires, other tires,buckets, storage vessels, drums, trays, measuring beakers, funnels,tanks, and housing parts.

The process of the invention is described using FIG. 1, but there is nointention that the invention be restricted thereto. FIG. 1 is a diagramof the surface of a thermoformed molding X, where the surface comprisesparticles P. (To simplify the presentation, only one particle isdepicted). The elevation formed by the particle itself has an aspectratio of about 0.71, this being the quotient calculated by dividing themaximum height mH of the particle, which is 5, since only that portionof the particle which protrudes from the surface of the molding Xcontributes to the elevation, by its maximum width mB, which in turn is7. A selected elevation of the elevations E present on the particles byvirtue of their fine structure has an aspect ratio of 2.5, this beingthe quotient calculated by dividing the maximum height mH′ of theelevation, which is 2.5, by its maximum width mB′, which in turn is 1.

The process of the invention is described using the examples below, butthere is no intention that the invention be restricted to thisembodiment.

EXAMPLE 1

A suspension of Aerosil R8200® (1% by weight in ethanol) is applied to athermoforming mold in a thermoforming machine (725, C. R. Carke & Co.),and the solvent (ethanol) is then evaporated. A molded sheet (0.5 mm)made from Vinnolit S 3257, a PVC with K value 57 is applied to the moldthus prepared, and is heated to the usual processing temperature forPVC. A vacuum is applied to thermoform the softened molded sheet. Afteradequate cooling, the vacuum pump is switched over to blowing, and theresultant molding is separated from the mold. This gives a molding whichcomprises microparticles anchored within the surface of the molding.

The roll-off angle for a water droplet from the resultant surface of themolding is determined by applying a droplet to the surface andprogressively increasing the inclination of the molding to determine theangle at which the droplet rolls off from the surface. For a waterdroplet of size 40 μl the roll-off angle obtained is 7.7°. An advancingangle of about 152° and a receding angle of 149.9° are also determined.These values show that the process of the invention can produce moldingswhich have self-cleaning surfaces.

1. A process for producing a molding comprising: accreting primaryparticles to form microparticles, wherein said microparticles havehydrophobic properties and said microparticles comprise agglomerates oraggregates of from 0.2 to 100 μm, applying the microparticles to theinner surfaces of a mold, molding a molding composition wherein themolding composition comprises at least one material comprising organiccompounds and said molding composition is in softened or molten form,and thermally shaping the molding composition in the mold, andsolidifying the molding composition to obtain the molding, wherein notmore than 90% of the diameter of at least 50% of the microparticles areimpressed into the surface of the molding which has not yet solidified,said microparticles are firmly held by the molding to anchor saidmicroparticles into the molding after the molding is solidified, saidmolding has elevations formed by the microparticles and said molding hasat least one surface having self-cleaning properties.
 2. The process asclaimed in claim 1, wherein said thermally shaping is at least oneprocess selected from the group consisting of blow molding, extrusionblow molding, extrusion stretch blow molding, injection blow molding,injection stretch blow molding, thermoforming, vacuum stretch forming,pressure stretch forming, and rotary thermoforming.
 3. The process asclaimed in claim 1 wherein said applying the microparticles is sprayingthe microparticles to the inner surfaces of the mold.
 4. The process asclaimed in claim 3, wherein said applying the microparticles is applyinga suspension, which comprises microparticles and at least one solvent,into the inner surfaces of the mold and then evaporating the solvent. 5.The process as claimed in claim 3, wherein said applying themicroparticles is applying an aerosol, which comprises microparticlesand at least one propellent gas, to the inner surfaces of the mold. 6.The process as claimed in claim 1, wherein the microparticles areselected from the group consisting of particles of silicates, minerals,metal oxides, metal powders, silicas, pigments, polymers and mixturesthereof.
 7. The process as claimed in claim 1 wherein the microparticlesare hydrophobicized fumed silicas.
 8. The process as claimed in claim 1,wherein said at least one material comprising organic compoundscomprises at least one material selected from the group consisting of anatural rubber, or a synthetic rubber, a vulcanized rubber,polynorbornene, poly-4-methyl-1-pentene, polyisobutene,acrylonitrile-butadiene-styrene terpolymers, polyvinylidene fluoride,polyalkylene terephthalates, polyacrylonitrile, polyether sulfones,polyesters, polystyrenes, cyclic polyalkenes, aliphatic linear branchedpolyalkenes, polypropylenes, polyethylenes, polyvinyl chloride,polyamides, polymethacrylates, polyacrylates, polycarbonates, acopolymer comprising at least one repeat unit selected from the groupconsisting of polynorbornene, poly-4-methyl-1-pentene, polyisobutene,acrylonitrile-butadiene-styrene terpolymers, polyvinylidene fluoride,polyalkylene terephthalates, polyacrylonitrile, polyether sulfones,polyesters, polystyrenes, cyclic polyalkenes, aliphatic linear orbranched polyalkenes, polypropylenes, polyethylenes, polyvinyl chloride,polyamides, polymethacrylates, polyacrylates and polycarbonates, andmixtures thereof.
 9. The process as claimed in claim 1, wherein themicroparticles are pressed into the surface of the molding which has notyet solidified, and the surface of the molding which has not yetsolidified is the surface of the molding composition in the molten form.10. The process as claimed in claim 1, wherein the microparticles arepressed into the surface of the molding which has not yet solidified,and the surface of the molding which has not yet solidified is thesurface of the molding composition in the softened form.
 11. A moldingproduced by a process as claimed in claim 1, wherein said molding has atleast one surface having self-cleaning properties and surface structureswith elevations.
 12. The molding as claimed in claim 11, wherein theelevations have an average height of from 20 nm to 25 μm and an averageseparation of from 20 nm to 25 μm.
 13. The molding as claimed in claim12, the elevations have an average height of from 50 nm to 4 μm and/oran average separation of from 50 nm to 4/m.
 14. The molding as claimedin claim 11, wherein the molding comprises microparticles and themicroparticles are selected from the group consisting particles ofsilicates, minerals, metal oxides, metal powders, silicas, pigments,polymers and mixtures thereof.
 15. The molding as claimed in claim 11,wherein the molding comprises impressed particles and the impressedparticles are anchored with from 10 to 90% of their average particlediameter within the surface of the molding.
 16. The molding as claimedin claim 11, wherein the molding is a three-dimensional article selectedfrom the group consisting of vessels, lampshades, buckets, bottles,tires, automotive tires, storage vessels, drums, dishes, measuringbeakers, funnels, tanks, splash guard components, discharge aids, andhousing parts.